JPS6111555B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless DC motor drive circuit.

In a DC motor, torque is generated that is proportional to the product of the field magnetic flux density and the motor coil current. Typically, the field flux pulsates with rotational position, resulting in deleterious torque ripple.

By the way, Japanese Patent Laid-Open No. 48-83323 discloses a method in which the pulsation of the field magnetic flux is detected and a current proportional to the reciprocal of the pulsation is passed through the motor coil, thereby keeping the product of the field density and the driving current constant. A motor control device is disclosed in which a constant torque is obtained by using a motor control device.

However, in general, in a DC motor, the field device is located on the stator side, so it is difficult to detect the pulsation of the field magnetic flux corresponding to the rotational position from the rotor side. Therefore, in the motor control device described in the above publication, the pulsation of the field magnetic flux is indirectly detected from the back electromotive force of the motor coil. However, since the back electromotive voltage includes the parameter of the motor rotation speed, it is necessary to separately obtain information on the motor rotation speed and detect the magnitude of the field magnetic flux based on the back electromotive voltage and the motor rotation speed information. Therefore, the detection circuit becomes complicated and the detection error is large, making it difficult to perform constant torque control accurately.

Therefore, it is conceivable to use a brushless DC motor, detect the pulsation of the field magnetic flux from the stator side, and flow a current proportional to the reciprocal of the magnetic flux density as described above. However, a brushless DC motor generally includes a plurality of independent switching elements for sequentially switching and driving multiple phase coils. Therefore, in order to drive a motor with a current proportional to the reciprocal of the magnetic flux density, it is necessary to detect the interlinkage magnetic flux of the coil for each phase and control the current for each switching element using a signal proportional to the reciprocal of each detection signal. There is a need to do. That is, it requires reciprocal calculation circuits and current control circuits for the number of phases, making the circuit configuration extremely complicated.

In addition, in order to share one reciprocal calculation circuit and current control circuit for each phase, the coil flux linkage detection signal obtained for each phase is synchronized with the on timing of the switching element of each phase and is derived to the reciprocal calculation circuit. A synchronization means is required. Therefore, the circuit configuration is also complicated in this case.

An object of the present invention is to improve the above-mentioned problem and to obtain a substantially constant motor torque by performing current drive proportional to the reciprocal of the interlinkage magnetic flux with a simple configuration.

The configuration of the present invention will be explained below along with examples.

In the present invention, a brushless DC motor is used to transfer the pulsation of the field magnetic flux to the stator.
It is designed so that it can be detected from the side. In addition, without incorporating any special magnetic flux detection means, the rotor rotational position detection element used to switch the energization of multiple phase motor coils according to the rotor rotational position is made of a magnetically sensitive type, and each coil is detected based on its output. The magnitude of magnetic flux linkage is detected.

In addition, the timing for switching the motor coils of multiple phases is always performed at the cross point (point where the levels match) of the output levels of the magnetic flux detection means of each phase, and in the energized phase, the output level of the magnetic flux detection means is the same as that of the other non-energized phases. Noting that the output level is always higher than the output level of the magnetic flux detection means, the levels of the respective output signals from the plurality of magnetic flux detection means are compared to obtain a maximum level signal having the maximum level. Since this maximum level signal represents the flux linkage density of the coil only in the energized phase, the linkage of the energized phase can be determined by deriving the maximum level signal to a single reciprocal calculation circuit without using a synchronization circuit. A signal proportional to the reciprocal of magnetic flux can be obtained. Therefore, if the magnitude of the current in the coils of each phase is commonly controlled based on this reciprocal proportional signal, it becomes possible to flow the reciprocal drive current in synchronization with the energization timing of the coils of each phase. In other words, the reciprocal calculation circuit and current control circuit are shared by each phase, which greatly simplifies the circuit configuration.

FIG. 1 is a schematic block diagram showing the principle of a DC brushless motor according to the present invention.

In FIG. 1, the rotational position of the rotor of a motor 1 is detected by a rotational position detection element 2. In FIG. This rotational position detecting element 2 is, for example, a Hall element, and detects leakage magnetic flux of a field magnet of the rotor. Therefore, the interlinkage magnetic flux B of the stator coil is B
If 〓=f(b〓), a detection signal E=k(b〓) approximately proportional to the interlinkage magnetic flux B of the stator coil of the motor 1 is obtained from the position detection element 2 (k: constant ). This detection signal E is supplied to a divider 3, where a signal F=proportional to the reciprocal of the signal E is
k'/(b〓) is formed (k': constant). This signal F is fed to a multiplier 4 (or a combination circuit), where a signal G is formed which is the product of the motor speed regulation voltage Vs and said signal F. Note that the motor speed adjustment voltage Vs may be a servo voltage or a constant DC voltage for controlling the speed of the motor.

Therefore, the output signal G of the multiplier 4 is G=
k′Vs/(b〓). This signal G is supplied to the voltage-current converter 5, so a transistor 6 for energizing the coil has a current i=(i)= proportional to the signal G.
I ₀ Vs/(b〓) (I ₀ : constant) flows. Therefore, the rotational torque generated by the current flowing through the coil and the interlinkage magnetic flux B ₀ of this coil is T=KZiB〓 =KZ・I ₀ Vs/(b〓)・(b〓)=KZI ₀ Vs (K: constant/Z: number of coil turns). That is, the rotational torque T is determined regardless of the coil's interlinkage magnetic flux density B = (b), and if the motor speed adjustment voltage Vs is constant, an almost constant rotational torque that is independent of the motor rotation angle θ is obtained. be able to.

Fig. 2 is a circuit diagram of a motor drive circuit in which the present invention is applied to a drive circuit of a three-phase, one-phase brushless DC motor, and Fig. 3 shows the waveforms of each part of Fig. 2 and the rotational torque of the motor. It is a graph.

In FIG. 2, Hall elements 2a, 2b, 2 which are magnetic flux detection means are used as the position detection element 2 of FIG.
c is used. These Hall elements 2a,
2b and 2c are attached to the stator side close to the magnet at a predetermined interval (for example, 120° interval) so as to be able to detect the leakage magnetic flux of the rotor magnet of the motor. These Hall elements 2
Resistors 11a, 12a, 11b, 12b, 11 are connected to a, 2b, 2c in the direction from the +V power supply to the ground potential.
A constant current is flowing through the terminals c and 12c.
The magnetic field of the rotor magnet acting in a direction perpendicular to this current generates an electromotive force between the output terminals of the Hall element in a direction perpendicular to both the current and the magnetic field. These Hall elements 2a, 2b, 2c
The electromotive force obtained between the output terminals of is negative feedback resistor 1
Differential amplifier 17 having 3a, 13b, 13c
a, 17b, and 17c. Therefore, from the outputs of the differential amplifiers 17a, 17b, 17c, the coils 16a, 16b, 16 as shown in FIG.
Almost sinusoidal detection signals Ea (solid line), Eb (dotted line), and Ec (dotted chain line) proportional to the interlinkage magnetic flux density of c are obtained, respectively. Note that these detection signals are each 120
It has a phase difference of °.

The detection signals Ea, Eb, and Ec are detected by the resistors 14a and 1
Transistors 20a, 20 via 4b, 14c
b and 20c, respectively. These transistors 20a, 20b, 20c, their load resistors 22a, 22b, 22c, and the common emitter resistor 15 constitute a differential amplifier, so that from the collector of each transistor there is a 120 Current switching signals Ha, Hb, and Hc are formed that switch by .degree. and have no overlapping portions. These current switching signals Ha, Hb, and Hc are supplied to the bases of drive transistors 21a, 21b, and 21c, respectively, so that these transistors
The three-phase coil 16 is turned on alternately in 120° increments.
A drive current is sequentially applied to a, 16b, and 16c.
Note that it is necessary to switch the energization at the level cross point of the detection signal in order to eliminate step fluctuations in torque and reduce torque ripple when switching phases.

On the other hand, the differential amplifiers 17a, 17b, 17
The detection signals Ea, Eb, and Ec of the outputs of diodes 19a, 19b, and 19c are supplied to a maximum signal level detection circuit 18 in which the cathodes of diodes 19a, 19b, and 19c are commonly connected. In this maximum signal level detection circuit 18, the detection signals Ea, Eb, and Ec applied to the anodes of the diodes 19a to 19c are compared with each other, and only the diode corresponding to the signal with the maximum level is turned on. , a maximum level signal E as shown in FIG. 3c is obtained. Diodes 19a-19c
The on-timing of is determined by the current switching signal in Figure 3b.
Consistent with Ha, Hb, and Hc. Therefore, only the interlinkage magnetic flux detection signal of the energized phase coil can be derived as the maximum level signal E. Since this maximum level signal E is proportional to the interlinkage magnetic flux density B = (b =) of each coil 16a, 16b, 16c, it can be expressed as E = k (b =) (k: constant, ( b〓) is a function of rotation angle θ). This signal E
is an operational amplifier 31, a transistor 45 and a resistor 3
The signal is supplied to a logarithmic conversion circuit 26 consisting of 6, where it is subjected to logarithmic conversion. Therefore, this logarithmic conversion circuit 26
A signal logE expressed as logE=log(b〓)+s is obtained from the output of (s: constant).
This signal logE is applied to the operational amplifier 3 via a resistor 38.
3 and one terminal of a subtraction circuit 28 consisting of a resistor 41.

On the other hand, the motor speed adjustment voltage Vs is supplied to a logarithmic conversion circuit 27 consisting of an operational amplifier 32, a transistor 46, and a resistor 37, where it is logarithmically converted. And the logarithmically converted signal logVs is the resistance 39
and 40, the subtraction circuit 2
It is supplied to the ten terminals of 8. As a result, subtraction circuit 2
From the output of 8, a signal J expressed as J=logVs−log(b〓)−s is obtained. This signal J is supplied to an antilogarithmic conversion circuit 29 consisting of a transistor 47, an operational amplifier 34, and a resistor 42, and a signal G expressed by G=k'Vs/(b〓) is obtained from this antilogarithmic conversion circuit 29. k′: constant). This signal G is connected to the operational amplifier 35, the resistors 43 and 44, and the transistor 4.
It is supplied to a voltage-current conversion circuit 30 consisting of 8. Therefore, a current i=(i)=I ₀ Vs/(b〓) flows through the transistor 48 according to the voltage level of the signal G (I ₀ : constant). Therefore, the coil 16a,
A current i expressed by the above equation is sequentially passed through each of 16b and 16c by 120 degrees. Therefore, the rotational torque T generated by this current i and the interlinkage magnetic flux density B of each coil is as follows: T=KZiB=KZ・I ₀ Vs/(b〓)・(b〓)=KZI ₀ Vs (K: constant/Z: number of coil turns). That is, the rotational torque of the motor is
Interlinkage magnetic flux density B ₀ = (b
〓) and is determined according to the speed adjustment voltage Vs. Therefore, no matter what magnetization pattern the rotor magnet has, if the speed adjustment voltage Vs is constant, it will produce a nearly constant rotational torque that is independent of the rotation angle θ of the motor, as shown in Figure 3e. You can get it. Therefore, torque ripple can be extremely reduced, and a motor without cogging can be obtained.

As described above, the present invention provides a motor drive circuit that detects the density of magnetic flux interlinking with the coil of a DC motor, performs reciprocal calculation of this detection signal, and causes a drive current to flow through the coil in accordance with this calculation output. In this system, the motor is a brushless DC motor so that the field magnetic flux can be detected from the stator side, and the field magnetic flux is detected using the output of the rotor position detection element for switching the energization of each phase coil. Therefore, the magnetic flux can be directly and accurately detected without performing inaccurate field detection based on the back electromotive force of the motor coil as in the past, and the field magnetic flux can be detected based on the detection output. By passing an inversely proportional motor drive current, a constant rotational torque with very little ripple can be obtained.

Furthermore, since the rotor position detecting element and the field magnetic flux detecting element are shared, a high-performance motor can be obtained with a simpler configuration without incorporating special magnetic flux detecting means into the motor.

Furthermore, the outputs of the plurality of magnetic flux detection means are compared with each other to obtain the maximum level signal, and the motor drive current is controlled by the reciprocal of this maximum level signal. Corresponding to the flux linkage density of the coil, it is possible to automatically obtain a flux linkage detection signal that matches the timing of energization switching without using any special synchronization means. The arithmetic circuit and current control circuit can be shared by each phase, resulting in an inexpensive and high-performance brushless DC motor.

In the example, a maximum level signal of positive polarity is obtained, but if a suitable polarity reversal circuit is used, it is possible to detect the maximum level signal of negative polarity among the magnetic flux detection signals Ea to Ec in Fig. 3a. This can be used for current control.

[Brief explanation of the drawing]

FIG. 1 is a schematic block circuit diagram showing the principle of a motor drive circuit according to the present invention, FIG. 2 is a circuit diagram of a motor drive circuit in which the present invention is applied to a three-phase, one-phase, brushless DC motor, and FIG. The figure is a graph showing the waveforms of each part of FIG. 2 and the rotational torque of the motor. In addition, in the symbols used in the drawings, 2a
~2c...Hall element, 16a-16c...Coil, 18...Maximum signal level detection circuit, 26,2
7... Logarithmic conversion circuit, 28... Subtraction circuit, 29...
. . . anti-logarithm conversion circuit, 30 . . . voltage-current conversion circuit.

Claims (1)

[Claims] 1. A brushless direct current device comprising a plurality of magnetic flux detection means for detecting magnetic flux linking to a plurality of coils, and a switching energization circuit for switching and energizing the coils based on output signals of the plurality of magnetic flux detection means. In the motor drive circuit, a maximum signal level detection circuit that compares the respective output signals from the plurality of magnetic flux detection means with each other, detects and outputs a signal having a maximum level, and an output from the maximum signal level detection circuit. A brushless DC motor, comprising: an arithmetic circuit that performs reciprocal calculations on signals; and a current control circuit that is commonly connected to the coils and supplies current to each coil based on the output signal of the arithmetic circuit. drive circuit.